Alkyl oligoglycosides are important surfactants since, being nonionic compounds, they are compatible with a large number of other ingredients, but exhibit a foaming and cleaning ability which is very much closer to that of anionic surfactants. Because of their good degradability and skin compatibility, they are used in cosmetics and in washing, dishwashing and cleaning compositions.
The starting materials used for their preparation are a glycose and branched, unbranched, and saturated and unsaturated alcohols, which are acetylated in the presence of acidic catalysts. To shift the reaction equilibrium, the alcohol is usually used in considerable excess. This results in reaction mixtures containing 20 to 50% alkyl and/or alkenyl oligoglycosides and 50 to 80% alcohol, which means that the resulting glycosides then have to be freed from unreacted alcohol at great technical expenditure before they can then be made into a paste with water and bleached.
Bleaching of the alkyl and/or alkenyl oligoglycoside is generally necessary since dark decomposition products form while the alcohol is being distilled off. Hitherto, the bleaching operation has only been possible with great technical expenditure.
European application EP 0 799 884 A2 (Unilever) describes liquid surfactant mixtures of alkyl and/or alkenyl oligoglycosides and ethoxylated nonionic surfactants in the weight ratio 35:65 and 65:35 and 2 to 25% water, and a process for the preparation of the surfactant mixtures. In the process, the bleaching agent used is a 30% strength aqueous hydrogen peroxide solution at temperatures of from 80 to 100° C. The content of water prior to bleaching should not be greater than 8% since more water is introduced as a result of the bleaching step. In the course of this process, water has to be added during the bleaching operation and accordingly be removed again. The surfactant mixtures of alkyl and/or alkenyl oligoglycosides and ethoxylated nonionic surfactants comprise at least 3.8% water. In contrast, the surfactant mixtures according to the invention are virtually anhydrous, i.e. are prepared with water contents of less than 2% by weight.
German patent specification DE 19543990 (Henkel) discloses liquid, anhydrous precursors for the preparation of washing, dishwashing and cleaning compositions which consist of alkyl and/or alkenyl oligoglycosides and alkyl polyglycol ethers in the weight ratio 10:90 and 90:10. Mixtures flowable at 40° C. which can be used in granulation processes for the preparation of laundry detergents are described.
German application DE 10019405 (Cognis), unpublished at the priority date of the present invention, describes anhydrous laundry detergent granules which comprise technical-grade mixtures of alkyl and/or alkenyl oligoglycosides and at most 30% by weight of fatty alcohol. These surfactant mixtures can be mixed or extruded together with laundry detergent additives.
The present invention is based on the object of developing a process for the preparation of light-colored alkyl and/or alkenyl oligoglycoside mixtures which avoids said disadvantages, in particular to prepare alkyl and/or alkenyl oligoglycoside mixtures with a low water content.
This is achieved by the content according to the invention of rheology-modifying agents, in particular by alcohol. This results in favorable rheology properties of the surfactant mixtures and these are thus accessible to a direct bleaching, without great technical expenditure, i.e. no aqueous alkyl and/or alkenyl oligoglycoside pastes have to be prepared by adding water for the bleaching. Using the process according to the invention, it is possible to prepare light-colored, high-concentration alkyl and/or alkenyl oligoglycoside-containing surfactant mixtures which are economically favorable both as a result of their preparation process and also with regard to transportation, thus saving energy and costs.